Not very many revolvers get treated with one of the spray-on finishes, sort of like how most BMWs aren't painted in latex house paint, with a brush. It just doesn't fit the application, and probably won't improve the look or value of the item.
However, if cost is the only factor, the painted finishes will at least keep a revolver from rusting, which is a plus, I guess. The biggest problem I see is that, while the paint will wear off in spots over time, it will be quite difficult to remove (usually requiring sand-blasting which is mighty hard on a revolver) when someone wants to restore the finish later.
However, if that's what you're going to do, no, do not allow the coating inside the chambers. That could make the gun non-functional on top of unsightly.